FIG. 4.

Quinolone-mediated DNA cleavage by S. pneumoniae gyrase (A) and topoisomerase IV (Topo IV) (B). Supercoiled pBR322 (0.4 μg) was incubated with S. pneumoniae GyrA (0.45 μg) and GyrB (1.7 μg) in the absence and presence of dimers 1, 2, and 3, ciprofloxacin (CIP), and pipemidic acid (PIP) at the indicated concentrations. After treatment with SDS and proteinase K, the DNA products were examined by electrophoresis in a 1% agarose gel. Lanes M, linear markers; lanes a and b, supercoiled and linear pBR322 DNA, respectively; lanes c, supercoiled pBR322 plus enzyme in the absence of drug but with 5 mM NaOH added. All the dimer reaction mixtures contained 5% dimethyl sulfoxide, and all ciprofloxacin reaction mixtures contained 5 mM NaOH. N, L, and S, nicked, linear, and supercoiled plasmid pBR322 DNA, respectively.